Unlocking the effect of Zn2+ on crystal structure, optical properties, and photocatalytic degradation of perfluoroalkyl substances (PFAS) of Bi2WO6

Bismuth tungstate (Bi2WO6) with a layered structure and visible light response exhibits excellent photocatalytic activity. To enhance its photocatalytic activity for the degradation of perfluoroalkyl substances (PFAS), Zn2+ is partially substituted for Bi3+ in the Bi2WO6 lattice in this study. Particularly, the effect of Zn2+ content (0-22.5 at%) on the crystal structure, optical property, and photocatalytic activity for the photodegradation of PFAS of Bi2WO6 is investigated. According to the Le Bail fits, the unit-cell volume is slightly reduced from 487.7 angstrom(3) to 480.8 angstrom(3) by the partial substitution of smaller Zn-2+ (0.74 angstrom for CN = 6) for larger Bi3+ (1.03 A for CN = 6) in the Bi2WO6 crystal lattice, and the solubility of Zn2+ in the Bi2WO6 lattice is found to be below 17.5 at%. The partial substitution of Zn2+ influences the self-aggregation of nanoparticles, Ostwald ripening, and self-organization of nanoplates, resulting in different morphologies. Although the optical bandgap energy of Bi2WO6 is not significantly altered upon the partial substitution of Zn2+, the conduction and valence bands simultaneously shift upward. Among the Bi2-xZnxWO6+delta photocatalysts, 2.5 at% Zn2+-substituted Bi2WO6 exhibits larger water oxidation photocurrent density (0.316 mA cm(-2) at 1.23 V-RHE) and the highest photocatalytic activity for the photodegradation of PFH(x)A (k(1) = 0.012 min(-1)). The trapping experiments confirm that the photo-excited holes (h(+)) and superoxide radicals (O-2(center dot-)) are the major reactive species involved in the photodegradation of PFH(x)A. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS) reveals that decarboxylation and defluorination are the main possible routes for the photodegradation of PFH(x)A over Bi2-xZnxWO6+delta photocatalysts. Our findings suggest that the partial Zn2+-to-Bi2+ substitution can enhance the photocatalytic activity of Bi2WO6 for the degradation of PFAS.

Automated summary

In this study, the photocatalytic activity of bismuth tungstate (Bi2WO6) for the degradation of perfluoroalkyl substances (PFAS) was enhanced by partially substituting Zn2+ for Bi3+ in the crystal lattice. The partial substitution of Zn2+ influenced the crystal structure, optical properties, and morphology of the nanoparticles of Bi2WO6, resulting in enhanced photocatalytic activity. The photodegradation of PFAS was mainly attributed to the photo-excited holes and superoxide radicals generated during the process.